The analysis of soil and liquid samples for potentially harmful materials has acquired greater importance as environmental awareness grows. One area of significant concern is the contamination of water and soil by petroleum by-products, such as gasoline and diesel fuels. The Environmental Protection Agency has set forth numerous regulations in the last decade, for instance, The Clean Water Act, requiring the testing of water and soil for contamination.
Several tests exist for determining the contamination of soil and/or water by pollutants, toxics and other contaminants, particularly volatiles and semi-volatiles. Such tests can be classified into one of three groupings. The first classification is known as Headspace Screening. In this method, either a solid or liquid sample, suspected of contamination, is placed into a container, such as a glass vial, and is heated to a temperature of about 150.degree. C. Volatile organic compounds are vaporized, escape to the headspace directly above the sample, and are extracted therefrom for analysis. A major deficiency in this method is that the sample must be contaminated to the extent that sufficient analyte be vaporized to the headspace. Hence, in this process, the detection limit is fairly high and samples having very low contamination cannot be adequately analyzed. A second disadvantage with the Headspace Screening method is that the extracted contaminants in the headspace typically rebind and complex with the water and moisture in the sample, thereby making it more difficult to detect low concentration of contaminants.
A second method is commonly referred to as the Purge and Trap Method. In this method, an aqueous sample is prepared from the contaminated source and place in a specially designed purging container at ambient temperature. Volatile organic compounds in the sample are converted from the aqueous phase to the vapor phase by the bubbling of an inert gas through the aqueous sample and swept to a sorbent trap. After purging is completed, the trap is heated and backflushed with the same inert gas to desorb the compound onto a gas chromatographic column whereupon the compounds are analyzed. The primary disadvantage is that the Purge and Trap method is capable of extracting and analyzing primarily light ends of hydrocarbons. Although some heavy ends also are extracted these compounds tend to collect as residual contamination in the trap. A related disadvantage in this method is that the trap must be cleaned with a solvent or changed after each contaminated use in order to cleanse the residual contamination from the trap.
A third method is the simple solvent extraction method, wherein an aqueous sample is admixed with a specific solvent designed to extract a particular analyte. The aqueous sample is shaken and the contaminants are separated from the sample. An essential drawback in this method is the use of solvents which are themselves pollutants of water and soil.
Among the widespread contamination of the water and the land, one of the more worrisome contaminations is caused by petroleum by-products. For instance, two common petroleum by-products typically found contaminating ground water, sludges and soil are gasoline and diesel. Accordingly, a method for Total Petroleum Hydrocarbons (TPH) analysis is required. Currently, TPH analysis cannot be efficiently performed by one simple method. Rather, two individual tests are required: (1) the analysis for volatile hydrocarbons (e.g. gasoline) which can be performed by the Headspace method or the Purge and Trap method and (2) the analysis for semi-volatile hydrocarbons (e.g. diesel) which is performed by the solvent extraction method. Because each of these methods is designed to primarily extract either volatiles or semi-volatiles, the analyst must employ two analytical procedures to determine whether contamination by gasoline and diesel fuels is present.
A number of processes have been disclosed in the prior art regarding extracting hydrocarbon contaminants from soil samples. For example, U.S. Pat. Nos. 2,165,440 and 2,212,681 teach a soil gas analysis wherein a soil sample is analyzed by the application of heat and vacuum in order to remove and sample the gas thereof. In U.S. Pat. No. 2,749,220, a method is disclosed for measuring gas in cones wherein a solid core is subjected to vacuum extraction in an evacuated chamber. Air is then mixed with the extracted gas in the chamber to form an air-gas mixture of known volume, and the proportion of hydrocarbon gas is thereafter determined.
Similarly, U.S. Pat. No. 2,799,561 discloses subjecting a solid core of soil to vacuum extraction in an evacuated chamber wherein a series of vacuum extractions is applied to a core sample which is being maintained under reduced pressure for a period of time following each extraction, in order to permit further volatilization of the liquid hydrocarbons in the sample.
U.S. Pat. No. 3,418,841 to Issenmann also provides a method of measuring and recovering gases from a sample of soil and the like by the use of heat in a vacuum.
In U.S. Pat. No. 3,539,209, a solvent extraction-type method is utilized, wherein earth samples are caused to release their content of hydrocarbon gases for analysis by treatment with a hot ethylenediamine tetraacetic acid solution. In U.S. Pat. No. 4,229,181, a sample of geological sediment is heated in intervals, to a first temperature range of 50.degree.-65.degree. C., a second temperature range of 200.degree.-350.degree. C., and a third and final temperature of 550.degree.-600.degree. C. Distinct hydrocarbons are released at successive stages.
Despite the teachings of the prior art, a need exists for a process for extracting pollutants, toxics and other impurities from virtually any sample wherein said sample can be analyzed for both volatiles and semi-volatiles from the same extraction process.